Reporting for duty

The Tektronix Phaser 3400N has a 17-ppm rating and parallel, USB and Ethernet ports. It's priced at $899.

The Tally T9412c prints 12 ppm and has parallel and USB ports. It's priced at $350.

Small laser printers shoulder the document load for many offices

Laser printers were amazing devices when Hewlett-Packard Co. first introduced them in 1984'about the same time PCs were getting hard drives.

They're still the paper generators of choice for most text documents'but these days all the printers from different vendors look pretty similar.

One major difference is whether the printer generates an image internally from a small, printer control language file, or downloads it from the PC as Microsoft Windows printers do.

Adobe Systems Inc. created desktop publishing when it introduced the PostScript page description language back in 1985. Until then, PCs sent text to all printers as ASCII code, and output depended entirely on a printer's internal fonts. Fonts printed on one device would look very different on another.

PostScript defines a font as a vector graphics image that can be displayed by a monitor, image-setter, or laser printer. This marked the birth of WYSIWYG desktop publishing.
Either the printer or the PC must convert the font description into a bitmap image before printing.

All the printers in the accompanying chart will run on a Windows PC, but Windows printers will only run under Windows because the bitmap image is created in the PC instead of the printer. The printer needs less memory and processing power, but during the printing cycle a large processor load is placed on the PC, which can slow response to a crawl. Print jobs are slowed even more because it takes time to transmit the data to the printer via the printer port.

When you consider just how big a letter-size bitmap file is, it's easy to see why fast, high-end laser printers cost so much.

Many monitors display images at 1,024- by 768-pixel resolution. This looks pretty good on screen but contains fewer than 800,000 pixels.

A screen image doesn't translate exactly to a printed page, so even at 300- by 300-dots-per-inch resolution, a letter-sized page contains about 10 times more pixels than a monitor image does.

At 600 dpi resolution the bitmap contains 30 million dots.

When a printer is used only occasionally, slow performance isn't a problem. That's when an inexpensive laser printer a good choice.

Electrified powder

In a true laser printer, the laser scans a fine point of light in a line on the light-sensitive drum. Drum rotation is indexed to the laser's control and, as the light plays on the drum, it imparts a static charge to the surface that picks up toner powder, creating an image on the drum. Paper is then charged and attracts the toner dust from the drum.

If the drum rotation is indexed in steps equal to one-three-hundredth of an inch, then you get 300 dpi vertical resolution. If the rotational precision is doubled, then you get 600 dpi. Horizontal resolution depends on how precisely the laser beam is moved across the drum's surface.

If you rub a bit of toner between your fingers, you'll notice that it feels oily or waxy. The final printing step is to heat the paper and ink in the fuser section, which, logically enough, fuses them by melting the wax.

The drum is then cleaned for the next image. A corona wire imposes a new charge on the entire drum, and a felt pad removes any remaining toner.

LED printers work the same way as laser printers except that, instead of scanning the print drum with a single laser beam, a strip of tiny light-emitting diodes transfers the image to the rotating drum.

In a 600-dpi printer, there are 600 individual LEDs to the inch for the entire width of the maximum paper capacity, normally 8.5 inches.

LED printers are mechanically simpler than lasers because they don't requiring a scanning mechanism. Hence they are smaller and less expensive.

The big disadvantage of LED printers is that the number of LEDs per inch limits their maximum horizontal resolution. A 600-dpi printer can produce a 300 dpi image, but it can't increase resolution to 1,200 dpi the way many laser printers can with just a software tweak of the scan rate.

LCD printers are similar but use a liquid crystal light source instead of LEDs.

All the static charges generated in laser printers generate a considerable amount of ozone, which is a major concern in a tiny office or where a number of printers are running together.

Some printers combat this with ozone filters, which are good for about 200,000 pages and then must be replaced.

EnergyStar printers also address environmental concerns by powering down the printer to a stand-by mode after a predetermined idle time. This greatly reduces power consumption at the expense of a small delay before the first page of a job can be printed. Virtually all laser printers have a standby mode, which cuts power consumption to less than 40 watts at idle.

If you use a printer only occasionally, it's best to simply turn it off between print jobs.
Power consumption rates are important only if the printer is used a lot or is left turned on all the time.

Pristine prints

Although all these printers produce good copy, you might need higher print quality, especially if the printer is used as a dedicated executive printer or the only printer in an office. Look at samples printed with the same fonts your documents will contain.

Up to a point, the amount of memory will determine how fast your printer can run, but this is usually a marginal difference'almost all printers have enough memory to perform up to their print engine's capabilities. The real need for larger memory comes when you download soft fonts to the printer. If you don't need this feature then extra memory is a waste.

The biggest difference between similarly priced laser printers is usually the ability to print a large number of pages. There is a specific limit on how many prints a unit can produce in a month. This is known as the duty cycle and, even for printers priced under $500, duty cycles range from as low as 2,500 to several hundred thousand pages per month.

You can view duty-cycle ratings as the difference between a pickup truck and a commercial truck'either one can haul gravel, but one can carry a lot more, day in and dayout, without breaking down.

But even 2,500 pages per month adds up to a lot of paper for a non-networked printer'100 pages every day for a business month. That means that most of these units can handle a small-office workload.

John McCormick is a free-lance writer and computer consultant. E-mail him at [email protected].

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